I made the mistake of washing my (home made) leaders and they really got wonky. The fabric shrunk differently in the main area than the hems and velcro areas. They also shrunk at an angle so my marking lines were off true perpendicular. My original HQ leaders are fine and will remain unwashed! I don't use them often because I prefer the shorter ones that I made when small quilts are being sewn.
I did redraw new reference lines on one set of my washed leaders so that they will work in a pinch, but I remade the size that I use most often (~66 inches)